arm64: implement CONFIG_STRICT_MEMORY_RWX for arm64

In order to improve security, protect the sections
the kernel uses for the 1-to-1 mapping of memory
as strictly as possible (i.e. no writing on text,
executing data, etc.)

Change-Id: I6ef6837502b8af4f914512f95ff902276e191351
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>